1. Field of the Invention
The present invention relates to heat exchangers, and more particularly to a laminated heat exchanger having a multiplicity of tube elements built up in layers.
2. Prior Art
A typical example of heat exchanger of this type is disclosed in Japanese Utility Model Publication No. 53-32375. The disclosed heat exchanger, as reillustrated here in FIG. 11 of the accompanying drawings, includes a tube element 1 composed of a pair of stamped plates 3 (only one shown) joined back to back with each there so as to provide a pair of juxtaposed tanks 4a, 4b at one end of the tube element 1. The tube element 1 has an elongate central partition wall 18 extending upwardly from the tanks 4a, 4b toward the opposite end of the tube element 1 so as to define a generally U-shaped channel 5 for the passage of a heat transferring medium. A plurality of such tube elements 1 are laminated or built up in layers with non-illustrated fins interposed between adjacent tube elements 1. The tube elements 1 and the fins are joined together by brazing under heated condition as in a hot oven. Preparatory to such mutual joining, each pair of adjacent tube elements are preassembled together in such a manner that side walls of the respective tanks 4 a, 4b and an upper joining flange (not shown but extending in a direction from the front toward the back of the sheet of drawing) of one tube element 1 are held in abutment with the tanks' side walls and the upper joining flange, respectively, of the other tube element 1.
The joining flange seems to be effective to hold the tube elements in a stably preassembled condition in which the tube elements are spaced at equal intervals or inter-element spaces. In general, in a heat exchanger of the type having tanks at only one end thereof, the tube elements are separated from one another at the other end of the heat exchanger because of interventing fins. The tube elements tend to be displaced, if not the joining flanges or the like clamping means.
Experiments uncovered the fact that the joining flanges held in abutment with each other are likely to bend or yield when subjected to forces or pressures applied in a facewise direction of the tube elements owing to some reason; during the brazing of the preassembled tube elements and the fins in a hot oven. With this deformation of the joining flanges, it is no longer possible to maintain the laminated tube elements in a uniformly spaced condition.
Since the channel 5 defined in each tube element 1 has a U-shape, a heat transferring medium reverses its direction of movement as it flows from one tank 4a to the other tank 4b along the U-shaped channel 5, the effective heat-exchanging area and the heat-exchanging efficiency of the heat exchanger are greater than that of another conventional heat exchanger having tanks disposed at opposite ends of each tube element.
A problem associated with the U-shaped channel 5 is that due to its tendency toward short-cut, the heat transferring medium flows more intensely in an inner region near the partition wall 18 than in an outer region remote from the partition wall 18, thus producing an outermost dead zone indicated by hatching. With this dead zone, the heat-exchanging efficiency of the heat exchanger is lowered to a certain extent.